PostgreSQL is designed to be
easily extensible. For this reason, extensions loaded into the
database can function just like features that are packaged with
the database. The contrib/ directory
shipped with the source code contains a large number of
extensions. The README file in that
directory contains a summary. They include conversion tools,
full-text indexing, XML tools,
and additional data types and indexing methods. Other extensions
are developed independently, like PostGIS. Even PostgreSQL replication solutions are
developed externally. For example, Slony-I is a popular master/slave replication
solution that is developed independently from the core
project.

There are several administration tools available for
PostgreSQL. The most popular is
pgAdmin III, and there are several
commercially available ones as well.